The present invention relates to an information sending system and method, which are characterized by the use of a specific data structure for outgoing information upon sending encrypted information.
Along with recent development of network techniques and spread of network communications, how to protect information flowing on a communication network such as a public network from an ill-disposed third party or the like is very important. For this reason, data and messages are encrypted in communications.
For example, a system for encrypting outgoing information (mail) so that only an authorized receiver can decrypt that information upon sending data, e-mails, or the like from an intra-office LAN to a destination outside the office is used.
However, when communications are made by encrypting data or messages using a network, it is hard to find out only whether or not the encrypted information is sensitive information such as a top secret of an enterprise, which must not leak outside the enterprise.
On the other hand, if a system for auditing all the contents of all the pieces of outgoing information from an intra-office LAN is built, not only the enterprise secret information but also personal e-mails must be audited. However, such system fails to protect privacy, and excessive information auditing may stall enterprise activities. Hence, a mechanism which can audit only specific information of those to be sent is demanded.
Meanwhile, service providers provide data distribution services for distributing chargeable digital contents such as music data, image data, and the like via a public network.
In such data distribution, in order to prevent free acquisition of the contents by a perpetrator, it is indispensable to encrypt data before distribution. In this case, it is convenient if a person who is considering subscription to a distribution service can get a sample of data contents to determine whether he or she would really like to purchase the contents.
Hence, a mechanism which can keep all kinds of information secret from an eavesdropper and allows a specific person who is a potential data purchaser to partially restore information is required.
It is an object of the present invention to provide an information sending system and method, which can send encrypted information which can be decrypted in units of portions of the information, i.e., stepwise, upon sending the encrypted information.
According to the first aspect of the present invention, there is provided an information sending system comprising information segmentation means for segmenting information into a plurality of blocks, first encoder for encrypting more than one blocks of the plurality of blocks using a first key, second encoder for encrypting more than one blocks of blocks other than the blocks encrypted by the first encryption means using a second key, and information sending means for sending outgoing information including the blocks encrypted by the first encoder and the blocks encrypted by the second encoder.
With this information sending system, blocks that form outgoing information are encrypted by different keys, and the outgoing information can be decrypted in units of blocks, i.e., stepwise.
According to the second aspect of the present invention, there is provided an information sending system comprising information segmentation means for segmenting information into a plurality of blocks, first encoder for encrypting more than one blocks of the plurality of blocks using a first key, second encoder for encrypting more than one block of blocks other than the blocks encrypted by the first encoder using a second key, information sending means for sending outgoing information including the blocks encrypted by the first encoder and the blocks encrypted by the second encoder, identification information appending means for appending, to the outgoing information, identification information indicating the blocks encrypted by the first encoder and the blocks encrypted by the second encoder of the blocks contained in the outgoing information, and key information appending means for appending, to the outgoing information, the encrypted first key, and the second key encrypted by an encryption key different from a key used for encrypting the first key.
With this information sending system, blocks that form outgoing information are encrypted by different keys, and the first and second keys for decrypting these blocks are encrypted by different keys and are added to the outgoing information. Hence, a person who has only a key that can decrypt the cryptograph of the first key can decrypt only the blocks encrypted by the first encoder, and a person who has both keys which can decrypt the cryptographs of the first and second keys can decrypt all the blocks of the received information.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.